The present invention relates to improvements made to the preform support devices designed to be combined with a multiplicity of similar devices articulately coupled together one after another into an endless chain for transferring preforms with simultaneous rotation of the latter on themselves, this device including:
a mounting plate provided with means of articulated coupling to two other adjacent mounting plates lying respectively to the front and to the rear (in the direction of movement of the chain); PA1 a body fixed to said mounting plate; and PA1 a rod supported by said body so as to rotate freely with the possibility of axial movement, said rod having a gripping end shaped in order to be removably fastened to the open end of a preform; PA1 the abovementioned coupling means including: PA1 a cavitied mounting plate 2 provided with means of articulated coupling to two other adjacent mounting plates lying respectively to the front and to the rear (in the direction (arrow 3) of movement of the transfer chain); PA1 a hollow body 4 fixed to the mounting plate 2; here, the body 4 consists of two parts, respectively an upper and a lower part, which are fixed in the mounting plate 2, for example, by screwing from above and from below the mounting plate, respectively; PA1 and a rod 5 supported so as to rotate freely in the hollow body 4; sleeves (shown, but not referenced) inside the body 4 guide the rod; furthermore, the rod is capable of being moved axially, with return by means of a spring 6. PA1 at the rear end of the mounting plate 2, a linking stem 11 supporting a spherical-cap-shaped coupling head 12, the spherical cap being, for example, convex with its convexity facing to the front, which is intended to bear on the adjacent mounting plate lying to the rear, PA1 at the front end of the mounting plate 2, a seat 13 in the form of a spherical zone having a shape complementary to the spherical cap, for example concave, and provided with a central axial opening 14 for the linking stem 11 of the adjacent it mounting plate, lying to the front, to pass through freely, the convex spherical cap of which bears on said concave seat. PA1 the spherical-cap-shaped coupling head is supported so as to rotate freely on the linking stem, PA1 a bearing plate is fastened, by fastening means, to the free end of the linking stem, this bearing plate extending transversely to the linking stem and substantially parallel to that face of the coupling head opposite its spherical-cap-shaped face, and PA1 an annular rolling bearing is interposed coaxially with the linking stem between the mutually facing faces of the coupling head and of the bearing plate. PA1 an axial recess of polygonal contour cut out in that face of the bearing plate opposite that carrying the rolling bearing, PA1 a radial groove cut out in the vicinity of the free end of the linking stem, and PA1 a retaining plate consisting of two parts joined together edge to edge along a transverse assembly edge, said retaining plate having a polygonal external contour complementary with that of the abovementioned recess and possessing a central orifice shaped to surround the linking stem, being engaged in the groove of the latter. PA1 the ability of the mounting plate to rotate about a horizontal axis is assigned to the rolling-bearing interface between the bearing plate and the coupling head; PA1 the ability of the mounting plate to rotate in the parts where the transfer chain bends is reserved just for the spherical head.
at a first end of the mounting plate, a linking stem supporting a spherical-cap-shaped coupling head intended to bear on the adjacent mounting plate lying on this first end side, and PA2 at a second end, a seat in the form of a spherical zone having a shape complementary to the abovementioned cap and provided with a central axial opening for the linking stem of the adjacent mounting plate, lying on this second end side, to pass through freely.
A preform transfer chain consisting of such devices is found especially in plants for manufacturing containers, such as bottles, flasks or the like, made of a plastic, especially a thermoplastic such as polyethylene terephthalate (PET). More particularly, a transfer chain formed in this way is used to move the preforms from a charging station up to and through a heating oven (tunnel oven) in which the material of which the preforms is made is heated in order subsequently to be molded, by a blow molding or stretch-blow molding process, into a large container (either the final container or an intermediate container). The transfer chain is furthermore designed so that the linear movement of the preforms is accompanied by a rotation of the preforms about themselves so that the material is heated uniformly all around the perimeter of the preforms, the heating means being arranged on one side in the oven.
FIG. 1 of the appended drawings represents, in diametral section, in a relatively detailed manner, a preform support device designed according to the usual technique, while FIG. 2 shows, from above, in a simplified form, the coupling parts (fraction of the transfer chain) of a group of three devices according to FIG. 1.
The preform support device, designated in its entirety by the reference 1, includes:
At its free end (at the bottom in FIG. 1), the rod 5 is provided with a gripping head 7 designed to be removably or releasably fastened to the open end of a preform 8 (in the drawing, the gripping head 7 is frictionally pressed into the opening in the preform 8).
At its opposite end (at the top in FIG. 1), the rod 5 is fastened to a toothed wheel 9 capable of meshing with a link chain (of the sprocket chain type) which extends fixedly along the path followed by the transfer chain, by virtue of which the rod 5, and therefore the preform 8 which it supports, is rotated about itself when the transfer chain moves in the direction of the arrow 3.
The axial movement of the rod 5 is obtained by means of a cam (not shown) brought under the toothed wheel 9.
The multiplicity of preform support devices coupled together one after another forms an endless transfer chain 10 (a fragment of which is shown diagrammatically in FIG. 2) which has to have an ability to articulate, especially, but not exclusively, in a horizontal plane (as shown diagrammatically in FIG. 1). However, in addition, suitable execution of the process for manufacturing the containers requires that the preforms be positioned in different attitudes at various points in the transfer: in particular, they are loaded opening up onto the support devices 1 but must be heated opening down in the oven and then must be brought back opening up at the exit of the oven in order to be transferred into the mold. As a result, each support device 1 needs to be able to rotate independently of the flanking devices to the front and rear, about a horizontal axis, through the action of external guide cams.
For these purposes, it is known that the means of coupling each support device 1 to the two adjacent devices to the front and rear comprise:
This known arrangement has certain drawbacks inherent in the structure adopted.
First of all, the spherical articulation thus formed bears, just by itself, the tensile forces during the movement of the transfer chain, as well as the frictional forces generated during the rotation of the mounting plates with respect to one another, both in the bends in the transfer chain and when inverting the position of the preforms. Admittedly, the seats 13 are coated with a layer of self-lubricating material having a low coefficient of friction, such as TEFLON, but, given the magnitude of the forces which are exerted and the high speeds at which the mounting plates are moving with respect to one another, this layer is rapidly worn away and the seats 13 must be refurbished.
Here too there is a problem since access to the seats, for the purpose of repairing them and/or replacing them, requires unfastening the coupled mounting plates. As shown in FIG. 2, each linking stem 11 has its end provided with a thread and the coupling head 12 is locked onto the linking stem 11 by means of a nut 15. Access to the nuts 15 is tight and inconvenient. In general, maintenance of the coupling means requires interrupting the operation of the plant which proves to be lengthy, given the difficulties in disconnecting and reconnecting, and which is therefore expensive because of the corresponding loss of production. There therefore exists a pressing need on the part of users of plants incorporating such transfer chains for a structure which, while still keeping the same operating capabilities, proves to be less subject to wear and has a simpler structure making it easier to disconnect and reconnect, so as to reduce the overall cost inherent in maintaining the chain. Furthermore, the spacing between successive preforms, and therefore between successive mounting plates, is determined by the overall arrangement of the plant and has been reduced to a minimum in current plants: it is therefore necessary not to upset this overall arrangement and to see to it that the improvements to be made to the mounting plates fall within the constraints of the preexisting free spaces.